This invention relates to the use of a method, a process, an apparatus and special chemicals to produce, inject and monitor the application of carbon disulfide-containing fluids. The apparatus efficiently combines carbon disulfide releasing chemicals in order to produce a carbon disulfide-containing paraffin dissolving chemical solvent for use in crude oil systems. More particularly, this invention relates to the chemical treatment of crude oil systems including: crude oil flow lines, pipelines, downhole production pumps, tubing and vessels. Carbon disulfide is effective at removing therefrom or preventing the forming of petroleum waxes commonly referred to as “paraffin deposits” or simply “paraffins.” The term “paraffin” as used to describe this problem refers to the deposit of carbonaceous material which is not soluble or dispersible by the crude oil under the conditions where deposition occurs. The “paraffin” normally consists of high molecular weight paraffin hydrocarbons, both straight chain and branched, resins and asphaltic materials of undetermined nature, occluded oil and water, and possibly oil-wet sand. In consistency, the deposit may vary from a soft, sticky material, to one which is hard and brittle. Paraffin deposits range in color from white to brown to black.
Under the conditions of temperature, pressure, and crude oil composition occurring in the underground reservoir, the paraffin is typically in suspension or solution in the crude. As the oil flows to the surface, there is generally a reduction of temperature, pressure, and the amount of dissolved gases contained in the oil. Reduction of temperature and gas break-out are shown to be factors causing reduced solubility of the paraffin in the crude oil. Thus, as the crude containing paraffin rises to the surface and flows to storage tanks through conduits at low pressure or atmospheric pressure, the solubility of the paraffin may be reduced. Deposition of paraffin will begin at the point in the system where the temperature of the system falls below its cloud point, or if the surface temperature of the crude oil piping falls below the cloud point, and continue if there is a further drop in the solvent power of the crude oil for the paraffin. The severity of the deposition in subsurface or surface equipment, will depend on the amount of paraffin originally in the crude oil, the way pressure and temperature of the crude oil are reduced and other properties of the crude oil and of the paraffin.
The melting point of the paraffin is the principal factor influencing solubility in each solvent, the solubility decreasing sharply with increased melting point, as would be expected. For hydrocarbon solvents, the main factor which influences solvent power is shown to be the American Petroleum Institute (“API”) gravity of the solvent, solvents of high API gravity being superior paraffin solvents, and solvents high in aromatic content.
Carbon disulfide is known to be one of the most effective solvents for dissolving paraffin of different compositions. However, use of carbon disulfide or carbon disulfide containing solvents in the field is difficult and hazardous because it is extremely toxic, odorous, flammable, and volatile. Carbon disulfide has a flash point of −22° F., a boiling point of 115.3° F., and an ignition temperature in air of 257° F. Carbon disulfide is highly soluble in oil.
Notwithstanding the physical handling challenges associated with carbon disulfide, there are several industrial applications. Carbon disulfide is a globally produced chemical solvent with the largest percentage of carbon disulfide produced today being used as a major raw material for the manufacture of regenerated cellulose. The two major products manufactured from regenerated cellulose are viscose rayon and cellophane. A considerable amount of carbon disulfide is also used in manufacturing carbon tetrachloride. Carbon disulfide is also used in the cold vulcanization of rubber and in making rubber accelerators and resins. In agriculture, carbon disulfide was widely used as a fumigant to control insects in stored grain, normally when mixed with other solvents to reduce the fire hazard.
Carbon disulfide is recognized by the Environmental Protection Agency as a potential neurotoxin. Workers physically handling carbon disulfide without protective gloves, eye and respiratory protection may be exposed to levels which may result in nerve damage.
Understanding and recognizing the concerns in handling carbon disulfide there is a real need in the oil & gas industry and other industries for a safe efficient method and process for producing, delivering and injecting carbon disulfide containing solvent into paraffin containing crude oils to remove paraffin deposits. This invention provides a safe method and process to produce carbon disulfide without possible exposure of carbon disulfide to workers and the environment. This inventive process uses a unique apparatus at or near the point of injection into crude oil systems including: oil & gas flowing pipelines or into an oil & gas producing wells to dissolve and remove paraffin deposits from within pipelines, vessels, downhole tubulars, and oil/gas/water separation equipment. More particularly, this invention relates to a process method to produce carbon disulfide safely at or near the point of injection without the typical dangers associated with the physical transporting, conveying or handling of carbon disulfide or solvent products containing carbon disulfide. The process uses a unique apparatus that produces carbon disulfide-containing fluid solvent on demand, eliminating the need to store carbon disulfide or carbon disulfide-containing treating chemical products on location.
Traditional treatments of the paraffin containing crude oil to dissolve paraffin deposits include: 1) mechanical scraping, 2) hot oiling, 3) hot water, 4) continuous application of heat, 5) chemical solvent batch treatments, 6) continuous paraffin inhibitor/solvent treatment, and 7) combination treatments of mechanical or thermal techniques. Still another less widely used method is the use of high strength magnets or electromagnets positioned in line to allow paraffin-containing oil to flow through an intense magnetic field to disrupt the paraffin's tendency to agglomerate and stick to the pipe walls.
U.S. Pat. No. 2,300,348 discloses a method wherein oil is heated and pumped downhole to thermally dissolve paraffin and remove it from the surface of production tubing and sucker rods. Many variations upon this method have been discovered and employed in later years. This basic hot oiling method continues today with crude oil system operators using hot oil heating equipment to dissolve paraffin downhole and on the surface in crude oil systems. The hot oil method is subject to many dangerous handling conditions when heating up a volatile crude oil using a propane or diesel fired burner. With many paraffin conditions, it has been discovered how repeated hot oiling of paraffin tends to remove the paraffin with lower melt points leaving behind the higher melt point paraffin. The high melt point paraffin builds up deposits on the internal surfaces of crude oil systems and makes it very difficult to remove mechanically, chemically or by requiring crude oil systems to use hot oil at much higher temperatures in order to dissolve the high melt point paraffin.
Chemical dissolution of paraffin deposits requires the application of aromatic and/or aliphatic solvents that will effectively and efficiently dissolve the paraffin regardless of structure, size and melting point. The process requires much less energy compared with thermally melting the wax. Typical solvents include chemicals based on condensate light gas oil, xylene, toluene, terpenes, and carbon disulfide. These solvents are generally pumped in the crude oil system in a batch slug volume or in a continuous injection method to remove paraffin from pipelines. In U.S. Pat. No. 3,241,614 it teaches a process for removing paraffin accumulations by contacting with liquid mixture of solvent and a surfactant. Various hydrocarbon solvents are mentioned, as is carbon disulfide. U.S. Pat. No. 3,375,192 teaches about a mixture for cleaning oil wells which is composed of carbon disulfide and pentane. U.S. Pat. No. 3,402,770 teaches about a single base solvent which is used to dissolve flow-restricting paraffin in oil well equipment. The solvent solution disclosed comprises of an organic solvent with carbon disulfide disclosed as the preferred organic solvent for oil and asphalt. In U.S. Pat. No. 3,563,315 it teaches the use of carbon disulfide used alone or in combination with hydrocarbon solvents or even present in low concentrations will aid in the removal of paraffin deposits from pipe wall surfaces.
In U.S. Pat. No. 3,724,552 (Snavely, Jr.), therein is described the use of water-soluble chemical selected from a class consisting of thiocarbonates, dithiocarbonates, and xanthates. In this patent, the inventor relies upon inexact mixing of the carbon disulfide releasing chemicals along with the elevated downhole temperatures and naturally acidic conditions caused by acid gases downhole to liberate carbon disulfide from these water-soluble compounds. Once the carbon disulfide is liberated it works to remove paraffin deposits from formations.
In U.S. Pat. No. 5,053,149 (McElligott Jr. et al) it describes a process for dissolving wax, paraffin and/or sulfur deposits in oil or gas pipeline or well involves the use of an acid and a compound which liberates carbon disulfide upon contact with the acid, whereby the deposit is dissolved by the liberated carbon disulfide. I this invention the inventor relies upon the inexact mixing of the carbon disulfide releasing chemicals combining with the addition of an acid to lower the pH and initiate the chemical reaction to release the carbon disulfide. The presence of crude oil, produced water and natural gas create an unknown mixture which lowers the efficiency in the release of the carbon disulfide which may lead to lower overall paraffin removal efficiency by using this method.
In U.S. Pat. No. 5,076,358 (Kissel) it teaches the use of one or more salts of tri- and tetrathiocarbonic acid injected into petroleum-bearing formations to form carbon disulfide to dissolve paraffin and increase flow of oil from the formation. The inventor here relies upon the inexact mixing of two chemicals in the presence of crude oil, produced water and natural gas to initiate and carry forward a reaction to release carbon disulfide from a carbon disulfide releasing chemical in a oil bearing reservoir.
In Canadian patent application CA 2,184,240 (Kissel) it teaches solutions of dithiocarbamate salts, such as the sodium salts of N-methyl dithiocarbamate and N, N-dimethyl dithiocarbamate, can be used as admixtures with acids to provide a non-corrosive treatment for oil production systems. It discloses how carbon disulfide lowers the pour point of the crude oil, reduces pressures in crude oil flow pipelines, reduces oil/water separation problems, and increases crude oil yields. The inventor describes the use of carbon disulfide in oil bearing formations to improve the production of oil and does not disclose a method or process to apply the carbon disulfide fluid into a crude oil system downhole or on the surface.
A need exists for a system which produces carbon disulfide-containing fluid in a mobile or easily transported modular system, able to control a chemical reaction using a class of carbon disulfide-releasing water soluble chemical compounds consisting of trithiocarbonates, dithiocarbamates, thiocarbonates, xanthates and dithiocarbonates. When the carbon disulfide-releasing chemical compounds are mixed in the process with an acid, organic or inorganic, where the pH of the blended fluid is reduced to below 3.5, the release of carbon disulfide occurs. The process can be operated in a continuous or intermittent continuous batch flow. The method and process occur in the unique apparatus located at or near the point of injection into the crude oil system. The process apparatus controls the physical conditions of the reaction including the temperature of the process and the proper metering and blending of the chemical compounds to achieve high efficiency in the release of carbon disulfide for injecting into crude oil system.